| Author |
Message |
Malcolm West (Ferrari_uk_tech)
Junior Member
Username: Ferrari_uk_tech
Post Number: 74
Registered: 7-2003
| | Posted on Thursday, August 28, 2003 - 2:22 am: | |
Is your problem at idle only - does the engine fire on eight cylinders when you come off the idle circuit, if you rev up the engine does it "pop and bang" as the revs come down? If this is the case I would see if you have a slow running jet blocked, or a blockage in the idle circuit in the carb - blowing through with an air line will clear the passage, also as already mentioned set the mixture screws so that the cylinder you are adjusting achieves maximum engine speed (as you turn the screw you will hear the engine increase or decrease in speed.
MW |
Don McCormick (Dandy_don)
Junior Member
Username: Dandy_don
Post Number: 90
Registered: 2-2002
| | Posted on Wednesday, August 27, 2003 - 11:08 pm: | |
Richelson,
I suggest that you back out all of the idle screws several turns just to see if that makes a difference to those cylinders firing. The basic procedure is to start with the idle screws backed out further than is necessary (way rich) and then slowly turn the idle screw in listening for the engine to stumble or falter (ie that cylinder stops firing as you have just closed off sufficient fuel to that cylinder to fire) After you have hit that point back the screw outwards a half turn or so and that approximates the correct idle mixture (exhaust gas analyzers will get you much closer to the correct mixture- but they cost a lot and this method is free if you do it yourself) I also would echo Drmike's thought about the vacuum leak at a cylinder causing the idle circuit to fail in that cylinder- I had exactly the same problem and it was corrected in 20 seconds by plugging the vacuum leak that I had inadvertently created. Good luck Don |
Mike Procopio (Pupz308)
Member
Username: Pupz308
Post Number: 500
Registered: 10-2002
| | Posted on Wednesday, August 27, 2003 - 9:36 pm: | |
Here are my results when I tested the plug wire resistance. 78 308.
Cylinder | Wire Resistance, Ohms | Wire Length, inches | Normalized Resistance, Ohms/inch
4 1573 26 60.5
3 1397 22 63.5
2 1058 18.5 57.18918919
1 681 15.5 43.93548387
The last column is the resistance per unit of distance one, which should be fairly consistent. I got 43 to 60 ohms/inch. I can't really explain the variance, other than I was in many cases estimating the length of the plug wires...
|
Dr. Mike Adams (Drmike)
New member
Username: Drmike
Post Number: 35
Registered: 5-2002
| | Posted on Wednesday, August 27, 2003 - 5:01 pm: | |
Watch out for a vacuum leak. A vacuum leak under a throat-per-cylinder weber setup can kill off enough of the vacuum signal to lean out or stop the idle circuit.
Just a thought. |
Paul (Pcelenta)
Member
Username: Pcelenta
Post Number: 398
Registered: 7-2002
| | Posted on Wednesday, August 27, 2003 - 4:18 pm: | |
10k per foot sounds right...when you test them it pays to wiggle them around a little to see if their are changes...on carb 308 with the black connectors there should be zero resistance in the extenders. |
JohnR. (Rivee)
Member
Username: Rivee
Post Number: 266
Registered: 1-2002
| | Posted on Wednesday, August 27, 2003 - 4:15 pm: | |
Richelson, you may have dirt in your idle jet seat. Pull out the idle jet screws(counting the turns to removal) and gently blow out the seats(low air press), or you could turn over the motor with them out
Also check the idle jet screws themselves for dirt or damage. Make sure they're not crooked.
Are the cylinders in question firing at a higher RPM?
Another thing happened to me was when I put new wires on the dist. cap I didn't use silicone to push them all the way into the cap hence wasn't making contact with the cap.
Regards,
John |
Richelson (Richelson)
Member
Username: Richelson
Post Number: 881
Registered: 12-2001
| | Posted on Wednesday, August 27, 2003 - 4:07 pm: | |
Ok. Do you happen to know the rule of thumb for plug wire resistance. Is it 10,000 per foot? I believe the extenders are 1,000 or so. Thank You for your help. |
Paul (Pcelenta)
Member
Username: Pcelenta
Post Number: 397
Registered: 7-2002
| | Posted on Wednesday, August 27, 2003 - 4:06 pm: | |
hey, just had similiar probs with my '78 gts last month...turned out it was a combo of a couple of 2 bad plug wires and a really bad coil wire that was providing weak spark to the plugs...check the continuity of your wires and resistance. I initially thought it was fuel in my case...replaced the pump, rebuilt all carbs...never thought the wires were going to be bad. Anyway, it is a place to start. |
Richelson (Richelson)
Member
Username: Richelson
Post Number: 880
Registered: 12-2001
| | Posted on Wednesday, August 27, 2003 - 2:51 pm: | |
I have a few cylinders down on my 308. I pulled the plug wire while the engine was running and the engine didn't change pitch. I checked for spark and I have spark. I believe I am not getting fuel through my idle circuit. One strange point is that on one carb I backed the idle jet out a few turns and it that cylinder started to fire. I checked the seating of the idle jet and it was in all of the way. I put a new o-ring on it and it made no difference. What does this mean? Any other ideas on why I am not getting fuel through some of my carbs on the idle circuit? Also could weak spark cause a cylinder not to fire at all? I had my spark gauge set to 20 (20,000V?) and the spark was more yellow than blue. Cleaned my cap contacts and rotor but it didn't help. Let me know if you gents have any solutions to these problems. |